Bi-fuel reciprocating engine to power direct drive turbine fracturing pumps onboard auxiliary systems and related methods

ABSTRACT

Systems and methods for supplying primary fuel and secondary fuel to an internal combustion engine may include supplying a first amount of the primary fuel and a second amount of the secondary fuel to the internal combustion engine. The system may include a first manifold to provide primary fuel to the internal combustion engine, and a primary valve associated with the first manifold to provide fluid flow between a primary fuel source and the internal combustion engine. A second manifold may provide secondary fuel to the internal combustion engine, and a fuel pump and/or a secondary valve may provide fluid flow between a secondary fuel source and the internal combustion engine. A controller may determine a total power load, the first amount of primary fuel, and the second amount of secondary fuel to supply to the internal combustion engine to meet the total power load.

PRIORITY CLAIM

This is a continuation of U.S. Non-Provisional application Ser. No.17/663,294, filed May 13, 2022, titled “BI-FUEL RECIPROCATING ENGINE TOPOWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMSAND RELATED METHODS,” which is a continuation of U.S. Non-Provisionalapplication Ser. No. 17/653,893, filed Mar. 8, 2022, titled “BI-FUELRECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPSONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” now U.S. Pat. No.11,365,616, issued Jun. 21, 2022, which is a continuation of U.S.Non-Provisional application Ser. No. 17/481,794, filed Sep. 22, 2021,titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINEFRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” nowU.S. Pat. No. 11,313,213, issued Apr. 26, 2022, which is a divisional ofU.S. Non-Provisional application Ser. No. 17/301,241, filed Mar. 30,2021, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINEFRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” nowU.S. Pat. No. 11,208,880, issued Dec. 28, 2021, which claims priority toand the benefit of, under 35 U.S.C. § 119(e), U.S. ProvisionalApplication No. 62/705,188, filed Jun. 15, 2020, titled “BI-FUELRECIPROCATING ENGINE TO POWER ONBOARD FRACTURING PUMP AUXILIARY SYSTEMSAND RELATED METHODS,” and U.S. Provisional Application No. 62/704,774,filed May 28, 2020, titled “SYSTEMS AND METHODS FOR SUPPLYING PRIMARYFUEL AND SECONDARY FUEL TO AN INTERNAL COMBUSTION ENGINE OF A FRACTURINGUNIT,” the disclosures of which are incorporated herein by reference intheir entireties.

TECHNICAL FIELD

The present disclosure relates to systems and methods for supplying fuelto an internal combustion engine of a fracturing unit and, moreparticularly, to systems and methods for supplying a primary fuel and asecondary fuel for operation of an internal combustion engine associatedwith a hydraulic fracturing unit.

BACKGROUND

Fracturing is an oilfield operation that stimulates production ofhydrocarbons, such that the hydrocarbons may more easily or readily flowfrom a subsurface formation to a well. For example, a fracturing systemmay be configured to fracture a formation by pumping a fracturing fluidinto a well at high pressure and high flow rates. Some fracturing fluidsmay take the form of a slurry including water, proppants, and/or otheradditives, such as thickening agents and/or gels. The slurry may beforced via one or more pumps into the formation at rates faster than canbe accepted by the existing pores, fractures, faults, or other spaceswithin the formation. As a result, pressure builds rapidly to the pointwhere the formation may fail and may begin to fracture. By continuing topump the fracturing fluid into the formation, existing fractures in theformation are caused to expand and extend in directions farther awayfrom a well bore, thereby creating flow paths to the well bore. Theproppants may serve to prevent the expanded fractures from closing whenpumping of the fracturing fluid is ceased or may reduce the extent towhich the expanded fractures contract when pumping of the fracturingfluid is ceased. Once the formation is fractured, large quantities ofthe injected fracturing fluid are allowed to flow out of the well, andthe production stream of hydrocarbons may be obtained from theformation.

Prime movers may be used to supply power to a plurality of fracturingpumps for pumping the fracturing fluid into the formation. For example,a plurality of gas turbine engines may each be mechanically connected toa corresponding fracturing pump and may be operated to drive thecorresponding fracturing pump. A fracturing unit may include a gasturbine engine or other type of prime mover and a correspondingfracturing pump, as well as auxiliary components for operating andcontrolling the fracturing unit, including electrical, pneumatic, and/orhydraulic components. The gas turbine engine, fracturing pump, andauxiliary components may be connected to a common platform or trailerfor transportation and set-up as a fracturing unit at the site of afracturing operation, which may include up to a dozen or more of suchfracturing units operating together to perform the fracturing operation.In order to supply electrical, pneumatic, and/or hydraulic power foroperation of the auxiliary components, an additional prime mover may beused. For example, another internal combustion engine may be used andmay have a relatively reduced rated output as compared to the primemover used for driving the fracturing pump. However, the additionalprime mover may have different fuel requirements, which may be costlyand/or may be prone to producing significant additional undesirableemissions. Thus, the additional internal combustion engine may increasecosts and result in higher emissions than desired.

Accordingly, Applicant has recognized a need for systems and methodsthat provide greater efficiency and/or reduced emissions when performinga fracturing operation. The present disclosure may address one or moreof the above-referenced drawbacks, as well as other possible drawbacks.

SUMMARY

The present disclosure generally is directed to systems and methods forsupplying fuel to an internal combustion engine associated with ahydraulic fracturing system. For example, in some embodiments, a systemto supply primary fuel and secondary fuel to operate an internalcombustion engine may include a first manifold positioned to providefluid flow from a primary fuel source of primary fuel to an internalcombustion engine. The system also may include a primary valveassociated with the first manifold and positioned to provide fluid flowbetween the primary fuel source and the internal combustion engine. Thesystem further may include a second manifold positioned to provide fluidflow from a secondary fuel supply of secondary fuel to the internalcombustion engine. The system still also may include one or more of afuel pump or a secondary valve associated with the second manifold andpositioned to provide fluid flow between the secondary fuel source andthe internal combustion engine. The system still further may include acontroller in communication with one or more of the primary valve, thefuel pump, or the secondary valve and may be configured to receive oneor more signals indicative of one or more of a hydraulic power load onthe internal combustion engine or an electric power load on the internalcombustion engine. The controller also may be configured to determine,based at least in part on the one or more signals, a total power load onthe internal combustion engine, and determine, based at least in part onthe total power load, a first amount of primary fuel to supply to theinternal combustion engine and a second amount of secondary fuel tosupply to the internal combustion engine. The controller further may beconfigured to cause, based at least in part on the first amount and thesecond amount, one or more of the primary valve, the fuel pump, or thesecondary valve to operate to supply the first amount of primary fueland the second amount of secondary fuel to the internal combustionengine.

According to some embodiments, a fracturing unit may include a chassisand a fracturing pump connected to the chassis and positioned to pump afracturing fluid. The fracturing unit also may include a gas turbineengine connected to the chassis and positioned to convert fuel into apower output for operating the fracturing pump. The fracturing unitfurther may include a reciprocating-piston engine connected to thechassis and positioned to supply power to operate one or more ofhydraulic auxiliary components or electrical auxiliary componentsassociated with the fracturing unit. The fracturing unit also mayinclude a first manifold positioned to provide fluid flow from a primaryfuel source of primary fuel to the gas turbine engine and thereciprocating-piston engine. The fracturing unit still may include asecond manifold positioned to provide fluid flow from a secondary fuelsupply of secondary fuel to the reciprocating-piston engine. Thefracturing unit additionally may include a controller configured toreceive one or more signals indicative of operation of one or more ofthe hydraulic auxiliary components or the electrical auxiliarycomponents, and determine, based at least in part on the one or moresignals, a first amount of primary fuel to supply to thereciprocating-piston engine and a second amount of secondary fuel tosupply to the reciprocating-piston engine. The controller also may beconfigured to cause, based at least in part on the first amount and thesecond amount, supply of the first amount of primary fuel and the secondamount of secondary fuel to the reciprocating-piston engine.

According to some embodiments, a method for supplying primary fuel andsecondary fuel to a reciprocating-piston engine may include determininga total power load on the reciprocating-piston engine due to operationof one or more of hydraulic auxiliary components supplied with power bythe reciprocating-piston engine or electrical auxiliary componentssupplied with power by the reciprocating-piston engine. The methodfurther may include determining, based at least in part on the totalpower load, a first amount of primary fuel to supply to thereciprocating-piston engine and a second amount of secondary fuel tosupply to the reciprocating-piston engine. The method further mayinclude causing, based at least in part on the first amount and thesecond amount, one or more of: a primary valve to operate to supply thefirst amount of primary fuel to the reciprocating-piston engine, or oneor more of a fuel pump or a secondary valve to operate to supply thesecond amount of secondary fuel to the reciprocating-piston engine.

Still other aspects and advantages of these exemplary embodiments andother embodiments, are discussed in detail herein. Moreover, it is to beunderstood that both the foregoing information and the followingdetailed description provide merely illustrative examples of variousaspects and embodiments, and are intended to provide an overview orframework for understanding the nature and character of the claimedaspects and embodiments. Accordingly, these and other objects, alongwith advantages and features of the present invention herein disclosed,will become apparent through reference to the following description andthe accompanying drawings. Furthermore, it is to be understood that thefeatures of the various embodiments described herein are not mutuallyexclusive and may exist in various combinations and permutations.

BRIEF DESCRIPTION OF THE DRAWINGS

The accompanying drawings, which are included to provide a furtherunderstanding of the embodiments of the present disclosure, areincorporated in and constitute a part of this specification, illustrateembodiments of the present disclosure, and together with the detaileddescription, serve to explain principles of the embodiments discussedherein. No attempt is made to show structural details of this disclosurein more detail than can be necessary for a fundamental understanding ofthe embodiments discussed herein and the various ways in which they canbe practiced. According to common practice, the various features of thedrawings discussed below are not necessarily drawn to scale. Dimensionsof various features and elements in the drawings can be expanded orreduced to more clearly illustrate embodiments of the disclosure.

FIG. 1 schematically illustrates an example fracturing system includinga plurality of hydraulic fracturing units, including a detailedschematic view of an example system for supplying primary fuel andsecondary fuel to an example internal combustion engine according to anembodiment of the disclosure.

FIG. 2 is a schematic view of an example system for supplying primaryfuel and secondary fuel to an example internal combustion engine toprovide power for example hydraulic auxiliary components and exampleelectrical auxiliary components according to an embodiment of thedisclosure.

FIG. 3 is a graph showing an example relationship of percentage ofprimary fuel supplied to operate an internal combustion engine as afunction of a percent of maximum power output by the internal combustionengine according to an embodiment of the disclosure.

FIG. 4 is a graph showing an example relationship of efficiency of aninternal combustion engine as a function of a percentage of maximumpower output by the internal combustion engine according to anembodiment of the disclosure.

FIG. 5 is a schematic view of another example fracturing systemincluding a plurality of hydraulic fracturing units receiving primaryfuel from an example primary fuel source according to an embodiment ofthe disclosure.

FIG. 6 is a block diagram of an example method for supplying primaryfuel and secondary fuel to a reciprocating-piston engine according to anembodiment of the disclosure.

DETAILED DESCRIPTION

The drawings include like numerals to indicate like parts throughout theseveral views, the following description is provided as an enablingteaching of exemplary embodiments, and those skilled in the relevant artwill recognize that many changes may be made to the embodimentsdescribed. It also will be apparent that some of the desired benefits ofthe embodiments described can be obtained by selecting some of thefeatures of the embodiments without utilizing other features.Accordingly, those skilled in the art will recognize that manymodifications and adaptations to the embodiments described are possibleand may even be desirable in certain circumstances. Thus, the followingdescription is provided as illustrative of the principles of theembodiments and not in limitation thereof.

The phraseology and terminology used herein is for the purpose ofdescription and should not be regarded as limiting. As used herein, theterm “plurality” refers to two or more items or components. The terms“comprising,” “including,” “carrying,” “having,” “containing,” and“involving,” whether in the written description or the claims and thelike, are open-ended terms, i.e., to mean “including but not limitedto,” unless otherwise stated. Thus, the use of such terms is meant toencompass the items listed thereafter, and equivalents thereof, as wellas additional items. The transitional phrases “consisting of” and“consisting essentially of,” are closed or semi-closed transitionalphrases, respectively, with respect to any claims. Use of ordinal termssuch as “first,” “second,” “third,” and the like in the claims to modifya claim element does not by itself connote any priority, precedence, ororder of one claim element over another or the temporal order in whichacts of a method are performed, but are used merely as labels todistinguish one claim element having a certain name from another elementhaving a same name (but for use of the ordinal term) to distinguishclaim elements.

FIG. 1 schematically illustrates an example fuel delivery system 10 forsupplying fuel to a plurality of hydraulic fracturing units 12,including a detailed schematic view of an example fuel line connectionassembly 14 according to embodiments of the disclosure. The fueldelivery system 10 may be part of a hydraulic fracturing system 16 thatincludes a plurality (or fleet) of hydraulic fracturing units 12configured to pump a fracturing fluid into a well at high pressure andhigh flow rates, so that a subterranean formation fails and begins tofracture in order to promote hydrocarbon production from the well.

In some examples, one or more of the hydraulic fracturing units 12 mayinclude directly driven turbine (DDT) pumping units, in which fracturingpumps 18 are connected to one or more gas turbine engines (GTEs) 20 thatsupply power to the respective fracturing pump 18 for supplyingfracturing fluid at high pressure and high flow rates to a formation.For example, a GTE 20 may be connected to a respective fracturing pump18 via a reduction transmission connected to a drive shaft, which, inturn, is connected to an input shaft or input flange of a respectivefracturing pump 18, which may be a reciprocating pump. Other types ofGTE-to-fracturing pump arrangements are contemplated.

In some examples, one or more of the GTEs 20 may be a dual-fuel orbi-fuel GTE, for example, capable of being operated using of two or moredifferent types of fuel, such as a gaseous fuel, for example, naturalgas, and a fluid fuel, for example, diesel fuel, although other types offuel are contemplated. For example, a dual-fuel or bi-fuel GTE may becapable of being operated using a first type of fuel, a second type offuel, and/or a combination of the first type of fuel and the second typeof fuel. For example, the fuel may include compressed natural gas (CNG),natural gas, field gas, pipeline gas, methane, propane, butane, and/orliquid fuels, such as, for example, diesel fuel (e.g., #2 Diesel),bio-diesel fuel, bio-fuel, alcohol, gasoline, gasohol, aviation fuel,and other fuels as will be understood by those skilled in the art.Gaseous fuels may be supplied by CNG bulk vessels, a gas compressor, aliquid natural gas vaporizer, line gas, and/or well-gas produced naturalgas. Other types and sources of fuel and associated fuel supply sourcesare contemplated. The one or more GTEs 20 may be operated to providehorsepower to drive via a transmission one or more of the fracturingpumps 18 to safely and successfully fracture a formation during a wellstimulation project or fracturing operation. Types of prime movers otherthan GTEs also are contemplated.

Although not shown in FIG. 1 , as will be understood by those skilled inthe art, the hydraulic fracturing system 16 may include a plurality ofwater tanks for supplying water for a fracturing fluid, one or morechemical tanks for supplying gels or agents for adding to the fracturingfluid, and a plurality of proppant tanks (e.g., sand tanks) forsupplying proppants for the fracturing fluid. The hydraulic fracturingsystem 16 may also include a hydration unit for mixing water from thewater tanks and gels and/or agents from the chemical tank to form amixture, for example, gelled water. The hydraulic fracturing system 16may also include a blender, which may receive the mixture from thehydration unit and proppants via conveyers from the proppant tanks. Theblender may mix the mixture and the proppants into a slurry to serve asfracturing fluid for the hydraulic fracturing system 16. Once combined,the slurry may be discharged through low-pressure hoses, which conveythe slurry into two or more low-pressure lines in a frac manifold 22, asshown in FIG. 1 . Low-pressure lines in the frac manifold 22 feed theslurry to the plurality of fracturing pumps 18 shown in FIG. 1 throughlow-pressure suction hoses.

FIG. 1 shows an example fuel delivery system 10 associated with aplurality, or fleet, of example hydraulic fracturing units 12 accordingto embodiments of the disclosure, although fewer or more hydraulicfracturing units 12 are contemplated. In the example shown, each of theplurality of hydraulic fracturing units 12 includes a GTE 20. Each ofthe GTEs 20 supplies power for each of the hydraulic fracturing units 12to operate a respective fracturing pump 18.

The fracturing pumps 18 are driven by the GTEs 20 of the respectivehydraulic fracturing units 12 and discharge the slurry (e.g., thefracturing fluid including the water, agents, gels, and/or proppants) athigh pressure and/or a high flow rates through individual high-pressuredischarge lines 24 into two or more high-pressure flow lines 26,sometimes referred to as “missiles,” on the frac manifold 22. The flowfrom the flow lines 26 is combined at the frac manifold 22, and one ormore of the flow lines 26 provide flow communication with a manifoldassembly, sometimes referred to as a “goat head.” The manifold assemblydelivers the slurry into a wellhead manifold, sometimes referred to as a“zipper manifold” or a “frac manifold.” The wellhead manifold may beconfigured to selectively divert the slurry to, for example, one or morewell heads via operation of one or more valves. Once the fracturingprocess is ceased or completed, flow returning from the fracturedformation discharges into a flowback manifold, and the returned flow maybe collected in one or more flowback tanks.

As shown in the detailed schematic view of an example system 28 forsupplying primary fuel and secondary fuel to an example internalcombustion engine 30 according to embodiments of the disclosure, one ormore of the hydraulic fracturing units 12 also may include hydraulicauxiliary components 32 and electrical auxiliary components 34 foroperating auxiliary components of the respective hydraulic fracturingunit 12, which may facilitate operation of the hydraulic fracturing unit12. For example, the hydraulic auxiliary components 32 may be configuredto supply hydraulic power for operation of hydraulic circuits on-boardthe hydraulic fracturing unit 12, as will be understood by those skilledin the art, including, for example, a hydraulic fluid reservoir, one ormore hydraulic pumps for providing the hydraulic circuits with power,one or more flow control valves, metering valves, or check valves,and/or one or more hydraulic actuators, such as hydraulic motors andhydraulic cylinders for preforming functions associated with operationof the hydraulic fracturing unit 12. The electrical auxiliary components34 may include one or more electrical power sources to provideelectrical power for operation of electrical circuits (e.g., anelectrical power generation device, batteries, solar panels, etc.),component controllers, instrumentation, sensors, and/or one or moreelectric actuators, such as electric motors and linear actuators, aswill be understood by those skilled in the art. Other hydraulic and/orelectrical components are contemplated.

In the example shown in FIG. 1 , one or more of the components of thehydraulic fracturing system 16 may be configured to be portable, so thatthe hydraulic fracturing system 16 may be transported to a well site,assembled, operated for a relatively short period of time, at leastpartially disassembled, and transported to another location of anotherwell site for use. Each of the fracturing pumps 18 and GTEs 20 of arespective hydraulic fracturing unit 12 may be connected to (e.g.,mounted on) a chassis. In some examples, the chassis may include aplatform or trailer (e.g., a flat-bed trailer) and/or a truck body towhich the components of a respective hydraulic fracturing unit 12 may beconnected. For example, the components may be carried by trailers and/orincorporated into trucks, so that they may be easily transported betweenwell sites.

As shown in FIG. 1 , the example fuel delivery system 10 may include aplurality of fuel line connection assemblies 14, for example, forfacilitating the supply of primary fuel from a primary fuel source 36 toeach of the GTEs 20 of the hydraulic fracturing system 16. In someembodiments, for example, as shown in FIG. 1 , one or more of the fuelline connection assemblies 14 may include a manifold line 38 providingfluid flow between the primary fuel source 36 and the respectivehydraulic fracturing units 12.

In the example shown in FIG. 1 , the fuel delivery system 10 includestwo hubs 40 a and 40 b (e.g., fuel hubs). A first one 40 a of the hubs40 a, 40 b is connected to the primary fuel source 36 via a first fuelline 42 a, and a second hub 40 b is connected to the primary fuel source36 via a second fuel line 42 b. The first hub 40 a may supply primaryfuel to one or more (e.g., each) of the GTEs 20 of a first bank 44 a ofhydraulic fracturing units 12, and the second hub 40 b may supplyprimary fuel to one or more (e.g., each) of the GTEs 20 of a second bank44 b of hydraulic fracturing units 12. Fewer (zero or one), or more,than two hubs are contemplated.

For example, as shown in FIG. 1 , the fuel delivery system 10 mayinclude a fuel line connection assembly 14 associated with each of thehydraulic fracturing units 12. In the example configuration shown inFIG. 1 , each of the hydraulic fracturing units 12 of the first bank 44a may be in fluid communication with the primary fuel source 36 via thefirst fuel line 42 a, the first hub 44 a, and a respective one of themanifold lines 38 providing fluid flow between the first hub 40 a andeach of the respective hydraulic fracturing units 12.

As shown in the detailed schematic view in FIG. 1 of the example system28 for supplying primary fuel and secondary fuel to an example internalcombustion engine 30, a fuel distribution line 46 may be connected tothe manifold line 38 to provide fluid flow between the manifold line 38and the GTE 20. In some examples, a fuel valve 48 may be provided in thefuel distribution line 46 to control the flow of primary fuel to the GTE20. In some examples, the system 28 may also include a filter 50disposed in the fuel distribution line 46 between the manifold line 36and the GTE 20 and configured to filter one or more of particulates orliquids from primary fuel flowing to the GTE 20. In some examples, thefilter 50 may include a first filter configured to remove particulatesfrom primary fuel supplied to the GTE 20 and a second filter (e.g., acoalescing filter) configured to remove liquids from the fueldistribution line 46 before primary fuel reaches the GTE 20. This mayimprove performance of the GTE 20 and/or reduce maintenance and/ordamage to the GTE 20 due to contaminants in the fuel as will beunderstood by those skilled in the art.

The example system 28 shown in FIG. 1 also includes a first manifold 52positioned to provide fluid flow from the primary fuel source 36 ofprimary fuel to the internal combustion engine 30. In some examples, andas shown in FIG. 1 , the internal combustion engine 30 may be connectedto the hydraulic auxiliary components 32 and/or the electrical auxiliarycomponents 34 to supply mechanical power to operate the hydraulicauxiliary components 32 and/or the electrical auxiliary components 34,as explained in more detail herein with respect to FIG. 2 .

As shown in FIG. 1 , a primary valve 54 may be provided in the firstmanifold 52 and may be configured to control the flow of primary fuelfrom the primary fuel source 36 to the internal combustion engine 30.The system 28 also may include a filter 56 disposed in the firstmanifold 52 between the manifold line 36 and the internal combustionengine 30 and configured to filter one or more of particulates orliquids from primary fuel flowing to the internal combustion engine 30.In some examples, the filter 56 may include a first filter configured toremove particulates from primary fuel and a second filter (e.g., acoalescing filter) configured to remove liquids from the first manifold52 before primary fuel reaches the internal combustion engine 30. Thismay improve performance of the internal combustion engine 30 and/orreduce maintenance and/or damage to the internal combustion engine 30due to contaminants in the fuel, for example. In some embodiments, thesystem 28 for supplying primary fuel and secondary fuel also may includea pressure regulator 58 disposed in the first manifold 52 between, forexample, the filter 56 and the primary valve 54 and configured tocontrol pressure of the primary fuel in the first manifold 52. Asexplained in more detail herein with respect to FIG. 2 , this examplearrangement may facilitate operation of the internal combustion engine30 using the primary fuel from the primary fuel source 36 shared withthe GTE 20 for operation.

As shown in FIG. 1 , the example system 28 shown also includes a secondmanifold 60 positioned to provide fluid flow from a secondary fuelsupply 62 of secondary fuel to the internal combustion engine 30. Forexample, the system 28 also may include a fuel pump 64 configured todraw and/or pump secondary fuel from the secondary fuel supply 62through the second manifold 60 to the internal combustion engine 30.Some embodiments also may include a secondary valve 66 disposed in thesecondary manifold 60 configured to control the flow of secondary fuelfrom the secondary fuel supply 62 to the internal combustion engine 30.The system 28 also may include a filter 68 disposed in the secondmanifold 60 between the fuel pump 64 and the secondary valve 66 andconfigured to filter one or more of particulates or liquids fromsecondary fuel flowing to the internal combustion engine 30. In someembodiments, the filter 68 may include a first filter configured toremove particulates from secondary fuel and a second filter (e.g., acoalescing filter) configured to remove liquids from the second manifold60 before secondary fuel reaches the internal combustion engine 30. Thismay improve performance of the internal combustion engine 30 and/orreduce maintenance and/or damage to the internal combustion engine 30due to contaminants in the fuel as will be understood by those skilledin the art.

As shown in FIG. 1 , the system 28, in some embodiments, still also mayinclude a controller 70 in communication with the primary valve 54, thefuel pump 64, and/or the secondary valve 66 and configured to controlthe flow of primary fuel from the primary fuel source 36 and secondaryfuel from the secondary fuel supply 62 to the internal combustion engine30. For example, the controller 70 may be configured to receive one ormore signals indicative of a hydraulic power load on the internalcombustion engine 30 and/or an electric power load on the internalcombustion engine 30. In some examples, the one or more signalsindicative of operation of the hydraulic auxiliary components 32 mayinclude one or more signals generated by one or more sensors associatedwith the hydraulic auxiliary components 32. In some examples, the one ormore signals indicative of operation of the electrical auxiliarycomponents 34 may include one or more signals generated by one or moresensors associated with the electrical auxiliary components 34. Forexample, operation of the hydraulic auxiliary components 32, suppliedwith power by the internal combustion engine 30, and/or operation of theelectrical auxiliary components 34, supplied with power by the internalcombustion engine 30, generate a power load on the internal combustionengine 30, and the internal combustion engine 30 responds to changes inthe power load to meet the power demands of the hydraulic auxiliarycomponents 32 and/or the electrical auxiliary components 34.

In some examples, the controller 70 may determine a total power load onthe internal combustion engine 30, for example, based at least in parton the one or more signals indicative of the hydraulic power load on theinternal combustion engine 30 and/or the electric power load on theinternal combustion engine 30. Based at least in part on the total powerload, the controller 70 may also determine a first amount of primaryfuel to supply to the internal combustion engine 30 and a second amountof secondary fuel to supply to the internal combustion engine 30. Basedat least in part on this determination of the total power load, thecontroller 70 may be configured to cause the primary valve 54,associated with the flow of primary fuel to the internal combustionengine 30, the fuel pump 64, and/or the secondary valve 66, associatedwith the flow of secondary fuel to the internal combustion engine 30, tooperate to supply the first amount of primary fuel and the second amountof secondary fuel to the internal combustion engine 30.

In this example manner, the system 28 may provide fuel for operationfrom two (or more) different fuel sources to the internal combustionengine 30 for operation. In some examples, the primary fuel may be agaseous fuel, such as, for example, compressed natural gas (CNG),natural gas, field gas, pipeline gas, methane, propane, and/or butane aswill be understood by those skilled in the art. Gaseous fuels may besupplied by CNG bulk vessels, a gas compressor, a liquid natural gasvaporizer, line gas, and/or well-gas produced natural gas. In someexamples, the primary fuel may be provided by the primary fuel source36, which, in some examples, is the same source of the primary fuelsupplied to the GTE 20. The secondary fuel, in some examples, may be aliquid fuel, such as, for example, diesel fuel (e.g., #2 Diesel),bio-diesel fuel, bio-fuel, alcohol, gasoline, gasohol, aviation fuel,and other fuels as will be understood by those skilled in the art. Thesecondary fuel may be supplied by the secondary fuel supply 62, whichmay be a fuel tank associated with the hydraulic fracturing unit 12 towhich the internal combustion engine 30 is connected.

Thus, in some examples, the system 28 may be configured to supply bothgaseous fuel and liquid fuel to the internal combustion engine 30 foroperation. Some examples of the internal combustion engine 30 may be areciprocating-piston diesel engine, or reciprocating-pistoncompression-ignition engine, which may be configured to operate usingthe primary fuel (e.g., natural gas), the secondary fuel (e.g., dieselfuel), or a combination of the primary fuel and secondary fuel. In someexamples, operation of the internal combustion engine 30 using primaryfuel that includes, or is limited to, natural gas may be relatively morecost-effective and/or may result in relatively reduced emissions ascompared to operation of the internal combustion engine 30 usingsecondary fuel that includes, or is limited to, diesel fuel. Thus,during operation in which the internal combustion engine 30 is able tosupply a sufficient amount of power using solely the primary fuel (e.g.,natural gas) supplied by the primary fuel source 36 to meet the powerdemands of the hydraulic auxiliary components 32 and/or the electricalauxiliary components 34, the system 28 may operate the internalcombustion engine 30 using solely the primary fuel supplied by theprimary fuel source 36, for example, to increase efficiencies and/orreduce emissions associated with operation of the internal combustionengine 30.

In some such examples of the internal combustion engine 30, operationusing solely the primary fuel (e.g., natural gas) may result in arelatively reduced maximum power output as compared to operation of theinternal combustion engine 30 using the secondary fuel (e.g., dieselfuel). Thus, for operational situations in which operation of theinternal combustion engine 30 using solely the primary fuel supplied bythe primary fuel source 36 would not result in supplying enough power tothe hydraulic auxiliary components 32 and/or the electrical auxiliarycomponents 34 to meet the power demands of the hydraulic auxiliarycomponents 32 and/or the electrical auxiliary components 34, the system28 may be configured to substitute secondary fuel (e.g., diesel fuel)supplied by the secondary fuel supply 62 for at least a portion of theprimary fuel (e.g., natural gas) to meet the demands of the hydraulicauxiliary components 32 and/or the electrical auxiliary components 34,for example, as explained in more detail herein. In some operationalsituations, the system 28 may be configured to operate the internalcombustion engine 30 using solely secondary fuel supplied by thesecondary fuel supply 62, for example, to achieve a maximum power outputof the internal combustion engine 30.

Although not shown in FIG. 1 , in some embodiments, the GTE 20 may alsobe configured to operate using two or more different types of fuel. Forexample, in addition to being configured to operate using primary fuelsupplied by the primary fuel source 36 (e.g., natural gas), someexamples of the GTE 20 may also be configured to operate using thesecondary fuel (e.g., diesel fuel) supplied by the secondary fuel supply62, or a combination of the primary fuel and secondary fuel. Thesecondary fuel supply 62 may be a fuel tank connected to the hydraulicfracturing unit 12 and/or an auxiliary fuel tank or tanker configured tobe in flow communication with the hydraulic fracturing unit 12, the GTE20, and the internal combustion engine 30. Thus, in some examples, asshown, the GTE 20 and the internal combustion engine 30 may shareprimary fuel supplied by the primary fuel source 36 with the GTE 20and/or may share secondary fuel supplied by the secondary fuel supply 62with the GTE 20. Other types and sources of fuel are contemplated.

In some embodiments, the controller 70 may be configured to cause thefirst amount of primary fuel to decrease relative to the second amountof secondary fuel as the total power load on the internal combustion 30increases. Because, in some examples, the secondary fuel supplied by thesecondary fuel supply 62 may provide relatively more energy per unitmass or volume than the primary fuel supplied by the primary fuel source36, as the load increases on the internal combustion engine, thecontroller 70 may increase the ratio of secondary fuel to primary fuelsupplied to the internal combustion engine 30 to meet the increasingpower load demand.

The controller 70 may, in some examples, may be configured to determinethe first amount or primary fuel and the second amount of secondary fuelbased at least in part on an efficiency of the primary fuel (e.g., anenergy efficiency and/or a financial efficiency associated with theprimary fuel) relative to an efficiency of the secondary fuel (e.g., anenergy efficiency and/or a financial efficiency associated with thesecondary fuel). For example, for operational situations in whichoperation of the internal combustion engine 30 using a combination ofprimary fuel and secondary fuel will provide a power output sufficientto meet the combined power demands from the hydraulic auxiliarycomponents 32 and/or the electrical auxiliary components 34, thecontroller 70 may be configured to determine the first amount of primaryfuel and the second amount of secondary fuel that meets the powerdemands with the highest efficiency.

In some examples, the controller 70 may be configured to determine theamount of primary fuel and the amount of secondary fuel for operationbased at least in part on efficiency data accessed from a table storedin memory correlating the efficiency of the primary fuel, the efficiencyof the secondary fuel, and/or the power output of the internalcombustion engine 30 operating using the primary fuel and the secondaryfuel. For example, such correlations may be based on calculationsaccording to theoretical, mathematical, and/or scientific determinationsas a function of the efficiency of the primary fuel, the efficiency ofthe secondary fuel, and/or the power output of the internal combustionengine 30 based on the combination of primary fuel and secondary fuel(e.g., a ratio of the amount of the primary fuel to the amount of thesecondary fuel). In some examples, such correlations may beempirically-derived and/or estimated based at least in part onhistorical operation, testing, and/or simulated operation of theinternal combustion engine 30.

In some embodiments, the controller 70 may be configured to determinethe first amount of primary fuel and the second amount of the secondaryfuel for operation of the internal combustion engine 30, based at leastin part on one or more formulas relating the efficiency of the primaryfuel, the efficiency of the secondary fuel, and/or the power output ofthe internal combustion engine using the primary fuel and the secondaryfuel. For example, such formulas may be derived according totheoretical, mathematical, and/or scientific determinations relating theefficiency of the primary fuel, the efficiency of the secondary fuel,and/or the power output of the internal combustion engine 30 based onthe combination of primary fuel and secondary fuel (e.g., a ratio of theamount of the primary fuel to the amount of the secondary fuel). In someexamples, such formulas may be empirically-derived and/or estimatedbased at least in part on historical operation, testing, and/orsimulated operation of the internal combustion engine 30. Duringoperation according to some examples, the amounts of primary and/orsecondary fuel may be determined real-time, during operation of theinternal combustion engine 30, for example, depending on the total powerdemand for operation of the hydraulic auxiliary components 32 and/or theelectrical auxiliary components 34.

According to some embodiments, the controller 70 may be configured todetermine first expected emissions generated during operation of theinternal combustion engine 30 using the first amount of primary fueland/or second expected emissions generated during operation of theinternal combustion engine 30 using the second amount of secondary fuel.For example, emissions generated by operation of the internal combustionengine 30 using the primary fuel may differ from emissions generated byoperation of the internal combustion engine 30 using secondary fuel.Thus, in some examples, the controller 70 may be configured to estimateor determine first expected emissions generated during operation of theinternal combustion engine 30 using the first amount of primary fueland/or second expected emissions generated during operation of theinternal combustion engine 30 using the second amount of secondary fuel.Based at least in part on this/these determination(s), the controller 70may be configured to optimize the ratio of the first amount of primaryfuel to the second amount of secondary fuel to achieve a desiredemissions level (e.g., a lowest emissions level overall or per unitpower output) during operation of the internal combustion engine 30.

In some embodiments, the controller 70 may be configured to determinethe first amount of primary fuel and the second amount of secondary fuelbased at least in part on emissions data from a table correlating thefirst expected emissions from operation using primary fuel, the secondexpected emissions using secondary fuel, and/or the power output of theinternal combustion engine 30 operating using the first amount ofprimary fuel and the second amount of secondary fuel. For example, suchcorrelations may be based on calculations according to theoretical,mathematical, and/or scientific determinations as a function of theexpected emissions due to operation using the primary fuel, the expectedemissions due to operation using the secondary fuel, and/or the poweroutput of the internal combustion engine 30 based on the combination ofprimary fuel and secondary fuel (e.g., a ratio of the amount of theprimary fuel to the amount of the secondary fuel). In some examples,such correlations may be empirically-derived and/or estimated based atleast in part on historical operation, testing, and/or simulatedoperation of the internal combustion engine 30.

In some embodiments, the controller 70 may be configured to determinethe first amount of primary fuel and second amount of the secondary fuelfor operation of the internal combustion engine 30, based at least inpart on one or more formulas relating the expected emissions fromoperation using the primary fuel, the expected emissions from operationusing the secondary fuel, and/or the power output of the internalcombustion engine using the primary fuel and the secondary fuel. Forexample, such formulas may be derived according to theoretical,mathematical, and/or scientific determinations relating the expectedemissions from operation using the primary fuel, the expected emissionsfrom operation using the secondary fuel, and/or the power output of theinternal combustion engine 30 based on the combination of primary fueland secondary fuel (e.g., a ratio of the amount of the primary fuel tothe amount of the secondary fuel). In some examples, such formulas maybe empirically-derived and/or estimated based at least in part onhistorical operation, testing, and/or simulated operation of theinternal combustion engine 30. During operation according to someexamples, the amounts of primary and/or secondary fuel may be determinedreal-time, during operation of the internal combustion engine 30, forexample, depending on the total power demand for operation of thehydraulic auxiliary components 32 and/or the electrical auxiliarycomponents 34.

In still other embodiments, the controller 70 may be configured to causethe internal combustion engine 30 to operate according to two or morephases, depending at least in part on the total power load from thehydraulic auxiliary components 32 and/or the electrical auxiliarycomponents 34. For example, the two or more phases may include a firstphase during which operation of the internal combustion engine 30 usinga combination of the first amount of primary fuel and the second amountof secondary fuel provides a power output at least equal to the totalpower load. The first amount of primary fuel may have an ability, whencombusted, to produce a specific amount of energy, and similarly, thesecond amount of the secondary fuel may have an ability, when combusted,to produce a specific amount of energy. In some examples, according tooperation during the first phase, the first amount of primary fuel andthe second amount of secondary fuel include an amount of energy at leastequal to the total power load. For example, during the first phase, ifthe internal combustion engine 30 is able to supply a sufficient amountof power without using solely the secondary fuel to meet the total powerdemand, the controller 70 may cause the internal combustion engine 30 tosubstitute an amount of primary fuel for an amount of the secondary fuelwhile still providing an amount of power sufficient to meet the totalpower load demanded, for example, as described herein.

In some embodiments, the two or more phases may include a second phase,for example, when the total power load is greater than a maximum amountof power output the internal combustion engine 30 is capable ofproducing using a combination of the primary fuel and the secondaryfuel. In some such examples, the controller 70 may be configured tocause operation of the internal combustion engine using solely secondaryfuel, so that the internal combustion engine 30 may operate to providean amount of power to meet the total power load demanded and/or provideits maximum power output.

In some embodiments of the system 28, during operation of the internalcombustion engine 30 according to the first phase, the controller 70 maybe configured to determine the first amount of primary fuel and thesecond amount of secondary fuel based at least in part on a firstefficiency of the primary fuel, a second efficiency of the secondaryfuel, a first expected emissions generated during operation of theinternal combustion engine using the first amount of primary fuel,and/or a second expected emissions generated during operation of theinternal combustion engine 30 using the second amount of secondary fuel.In some examples, the effect of the efficiencies and/or emissions may beweighted, for example, to cause the effects to have a different level ofinfluence on the outcome of the determination. For example, it may bedesirable to achieve an operational efficiency of the internalcombustion engine 30 that is above a threshold, and thus, the effects ofthe efficiencies of the primary and secondary fuel may be weightedrelatively more heavily in the determination than the effects ofemissions. Under some circumstances, the effect on emissions may beweighted relatively more heavily, for example, to reduce emissions to alevel below a predetermined threshold, for example, to comply withgovernment standards or regulations associated with emissions due tooperation of the internal combustion engine 30.

FIG. 2 is a schematic view of an example system 28 for supplying primaryfuel and secondary fuel to an internal combustion engine 30 to providepower for example hydraulic auxiliary components 32 and exampleelectrical auxiliary components 34 according to embodiments of thedisclosure. As shown in FIG. 2 , some examples of the internalcombustion engine 30 may include a turbocharger 72 including a turbine74 and a compressor 76 connected to the turbine 74 and configured to bedriven by the compressor 76 during operation of the internal combustionengine 30, thereby increasing the intake pressure of the internalcombustion engine 30 during operation to increase power output. Forexample, the internal combustion engine 30 may include an exhaust system78, including an exhaust manifold 80 and an exhaust conduit 82 providingexhaust flow between the exhaust manifold 80 and the turbine 74 of theturbocharger 72.

During operation of the internal combustion engine 30, exhaust gasgenerated during combustion flows to the turbine 74 via the exhaustmanifold 80 and the exhaust conduit 82, and energy in the exhaust gas isimparted to the turbine 74, causing it to spin and drive the compressor76, which is in flow communication with an intake conduit 84, whichsupplies the compressed air to an intake manifold 86 of the internalcombustion engine 30. Ambient intake air 88 is supplied via an intake 90and the intake conduit 84 to the compressor 76 for compression. Asshown, some examples, of the internal combustion engine 30 include anair filter 92 configured to remove or separate particulates from the airdrawn into the intake 90.

As shown in FIG. 2 , in some embodiments, the system 28 is configuredsuch that the first manifold 52, which provides fluid flow between theprimary fuel source 36 and the internal combustion engine 30 through theprimary valve 54, intersects and feeds the intake conduit 84 upstream ofthe compressor 76 of the turbocharger 72, such that the primary fuelmixes with the ambient air in the intake conduit 84 prior to beingcompressed by the turbocharger 72. Once compressed by the compressor 76,the air and primary fuel mixture flows to the intake manifold 86, whereit can be distributed for combustion in the internal combustion engine30.

As shown, secondary fuel from the secondary fuel supply 62 may be pumpedvia the fuel pump 64 via the second manifold 60 through the secondaryvalve 66 to a fuel rail 94 and thereafter injected under pressure viafuel injectors directly into one or more cylinders 96 (e.g., into thecombustion chambers) of a cylinder block 98 of the internal combustionengine 30. When operating using both primary fuel and secondary fuel,the primary fuel entering the intake manifold 86 and the secondary fuelentering the fuel rail 94, may be combined in the cylinders 96 (e.g., inthe combustion chambers) for combustion by the internal combustionengine 30. By controlling operation of the primary valve 54, the fuelpump 64, and/or the secondary valve 66, the controller 70 is, in someexamples, able to cause the internal combustion engine 30 to operateusing solely primary fuel, solely secondary fuel, and/or a combinationof primary fuel and secondary fuel. As explained previously herein, thecontroller 70 may be configured change the ratio of the amount ofprimary fuel to the amount of secondary fuel, for example, based on aload on the internal combustion engine 30, efficiencies associated withthe primary fuel and/or the secondary fuel, and/or expected emissionsfrom operation using the primary fuel and/or the secondary fuel.

As shown in FIG. 2 , the hydraulic auxiliary components 32 may includeone or more hydraulic pumps 100 and one or more hydraulic components102. For example, the hydraulic auxiliary components 32 may beconfigured to supply hydraulic power for operation of hydraulic circuitson-board the hydraulic fracturing unit 12 including, for example, ahydraulic fluid reservoir, the one or more hydraulic pumps 100 forproviding the hydraulic power to operate one or more of the hydrauliccomponents 102, which may be incorporated into hydraulic circuits, suchas flow control valves, metering valves, check valves, and/or one ormore hydraulic actuators, such as hydraulic motors and hydrauliccylinders for preforming functions associated with operation of thehydraulic fracturing unit 12. Other hydraulic components arecontemplated.

The example electrical auxiliary components 34 shown in FIG. 2 includesone or more electric power generation devices 104 and one or moreelectrical components 106. For example, the electrical auxiliarycomponents 34 may include one or more electrical power generationdevices 104 (e.g., alternators, generators, batteries, solar panels,etc.) for operation of electrical circuits including electricalcomponents 106 associated with operation of the hydraulic fracturingunit 12, such as component controllers, instrumentation, sensors, and/orone or more electric actuators, such as electric motors and linearactuators. Other electrical components are contemplated.

FIG. 3 is a graph 300 showing an example relationship of percentage ofprimary fuel supplied to operate an internal combustion engine 30 as afunction of a percentage of maximum power output by the internalcombustion engine 30 as represented by the line 302, according to anembodiment of the disclosure. As shown in FIG. 3 , in some examples, thecontroller 70 may be configured to begin substituting primary fuel forsecondary fuel at a power output of about 10 percent of the maximumpower output of the internal combustion engine 30. In some examples, thecontroller 70 may be configured to begin substituting primary fuel forsecondary fuel at a power output ranging from about 10 percent to about30 percent (e.g., ranging from about 20 percent to about 25 percent) ofthe maximum power output of the internal combustion engine 30.

As shown in FIG. 3 , the controller 70 may be configured to increase theamount of substitution of primary fuel for secondary fuel as the poweroutput of the internal combustion engine 30 increases from about 10percent to about 50 percent of the maximum power output, with thepercentage of primary fuel rising to an amount ranging from about 70percent to about 80 percent. In the example shown, the controller 70 maybe configured to substantially maintain the substitution rate of primaryfuel for secondary fuel at a range of about 70 percent to about 80percent at a power output ranging from about 50 percent to about 80percent of the maximum power output of the internal combustion engine 30(e.g., from about 50 percent to about 65 percent or 70 percent).Beginning at about 65 percent to about 80 percent of the maximum poweroutput of the internal combustion engine 30, the controller 70 may beconfigured to begin reducing the rate of substitution of primary fuelfor secondary fuel, and by about 85 percent to about 95 percent of themaximum power output, the controller 70 may be configured to reduce therate of substitution of primary fuel for secondary fuel to about zero.In some examples of the internal combustion engine 30, the primary fuel,and the secondary fuel, the internal combustion engine 30 may not becapable of a power output of greater than about 85 percent to about 95percent of maximum power during operation using any primary fuel, andthus, in some such examples, the controller 70 may be configured tocease substitution of primary fuel for secondary fuel at power outputsgreater than about 85 percent to about 95 percent of maximum power, sothat the internal combustion engine 30 operates solely using secondaryfuel to achieve the desired power output. For example, the primary fuelmay not have a sufficient amount of potential energy per unit volume forthe internal combustion engine 30 to operate close to its maximum poweroutput, while in contrast, the secondary fuel may have a sufficientamount of potential energy per unit volume for the internal combustionengine 30 to operate close to, or at, its maximum power output.

As shown in the example of FIG. 3 , in instances in which operating theinternal combustion engine 30 using primary fuel is relatively moreefficient (e.g., with respect to cost) than operating the internalcombustion engine 30 using secondary fuel, it may be desirable, withrespect to efficiency, to operate the internal combustion engine 30 at apower output ranging from about 40 percent to about 80 percent (e.g.,from about 45 percent to about 70 percent) of the maximum power outputof the internal combustion engine 30, such that the amount of primaryfuel substituted for secondary fuel is substantially maintained at anamount ranging from about 60 percent to about 80 percent. Differentranges of power output and/or substitution rates of primary fuel forsecondary fuel are contemplated, depending, for example, on the internalcombustion engine 30, the primary fuel, and/or the secondary fuel.

FIG. 4 is a graph 400 showing an example relationship of efficiencyassociated with operation of an internal combustion engine 30 as afunction of a percentage of maximum power output by the internalcombustion engine 30 as represented by the line 402, according to anembodiment of the disclosure. FIG. 4 shows a reduction in efficiency asan increase along the Y-axis of the graph 400 as a unit-less magnituderanging from about 2 to about 7.5. The efficiency may be determined, forexample, based at least in part on one or more factors, such as powerusage, cost of operation (e.g., including fuel cost), time to deliveryof power output, type or types of fuel(s) used for operation, thesuitability of the fuel(s) for operation, the completeness of combustionof the fuel(s), the quality of the fuel(s), and/or the emissionsgenerated during combustion of the fuel(s).

For example, as shown in FIG. 4 , a reduction in efficiency may occur asthe internal combustion engine 30 increases its power output, shown onthe X-axis as a percentage of the maximum power output of the internalcombustion engine 30. Thus, in general, in the example shown, as thepower output of the internal combustion engine 30 increases, itsefficiency may be thought of as decreasing, for example, becauserelatively more fuel may be required to operate the internal combustionengine 30 at relatively higher power outputs. This does not preclude thepossibility that, in some examples, operation of the internal combustionengine 30 at relatively higher power outputs may be relatively moreefficient, for example, due to the power output being a greaterpercentage of the maximum possible power output due to the potentialenergy of the fuel or fuels supplied to the internal combustion engine30 for operation (e.g., due to more complete combustion).

In some examples, a reduction in efficiency may occur as the internalcombustion engine 30 increases its power output, as shown in FIG. 4 ,which may correlate to an increase in cost of operation of the internalcombustion engine 30 due, for example, to the cost of the secondary fuelbeing relatively more expensive per unit volume than the cost of primaryfuel per unit volume. Thus, in general in the example shown, as moreprimary fuel is substituted for secondary fuel, the reduction inefficiency (e.g., the increase in cost) does not increase as quickly asthe internal combustion engine 30 is operated at a higher percentage ofits maximum power output and more total fuel is required to produce agreater power output by the internal combustion engine 30. Thus,although the cost increases due to the increase in power output (e.g.,the reduction in efficiency increases), by using a greater percentage ofprimary fuel, which costs less per unit volume than the secondary fuelin the example, the rate of increase in cost is reduced, with the rateof increase in cost being represented by the slope of the line 402.

In some embodiments, as shown in FIG. 4 , as the load on the internalcombustion engine 30 increases, such that the percentage of the maximumpower output of the internal combustion engine 30 at which the internalcombustion engine 30 operates increases to meet the increasing load, theefficiency reduction of operation of the internal combustion engine 30increases (e.g., the cost increases), as shown by the upward trend inline 402 as the power output increases. For example, when the internalcombustion engine 30 is operated at a power output ranging from lessthan about 40 percent of maximum power output to less than about 80percent of the maximum power output, the internal combustion engine 30is able to be operated using an increasing percentage of the primaryfuel (from less than about 60 percent to about 70 percent primary fuel)and a corresponding decreasing percentage of the secondary fuel. Atoperation above 80 percent maximum power output, in order to supply apower output sufficient to meet the increasing load on the internalcombustion engine 30, in some embodiments, operation reverts tooperation using solely (e.g., 100 percent) the secondary fuel, forexample, because the primary fuel does not have sufficient energy tomeet the load demands by operating at above 80 percent of maximum poweroutput, for example, as explained with respect to FIG. 3 . Under thesecircumstances, according to some embodiments, if use of the secondaryfuel for operation is less efficient (e.g., less cost-effective) thanuse of the primary fuel, the efficiency reduction increases, forexample, as shown by the slope of line 402 increasing as the internalcombustion engine 30 is operated at a power output above about 75percent to about 80 percent of the maximum power output of the internalcombustion engine 30.

FIG. 5 is a schematic view of another embodiment of a hydraulicfracturing system 16, including a plurality of hydraulic fracturingunits 12 receiving primary fuel from an example primary fuel source 36according to embodiments of the disclosure. In the example shown in FIG.5 , the original source of the primary fuel is a wellhead 500 of anatural gas well located close to the hydraulic fracturing system 16,which may provide a convenient and/or cost-effective source of theprimary fuel. In some such examples, natural gas may flow to a scrubberand filtration system 502 via a first gas fuel line 504 and thereafterflow to the primary fuel source 36 via a second gas fuel line 506.Thereafter, the primary fuel may flow from the primary fuel source 36via the first fuel line 42 a and the second fuel line 42 b, for example,similar to as shown in FIG. 1 . Other fuel delivery arrangements arecontemplated, such as, for example, “daisy-chain” arrangements,“hub-and-spoke” arrangements, combination “daisy-chain” and“hub-and-spoke” arrangements, and/or modifications of such arrangements.

FIG. 6 is a block diagram of an example method 600 for supplying primaryfuel and secondary fuel to a reciprocating-piston engine according toembodiments of the disclosure, illustrated as a collection of blocks ina logical flow graph, which represent a sequence of operations that maybe implemented in hardware, software, or a combination thereof. In thecontext of software, the blocks represent computer-executableinstructions stored on one or more computer-readable storage media that,when executed by one or more processors, perform the recited operations.Generally, computer-executable instructions include routines, programs,objects, components, data structures, and the like that performparticular functions or implement particular data types. The order inwhich the operations are described is not intended to be construed as alimitation, and any number of the described blocks can be combined inany order and/or in parallel to implement the methods.

FIG. 6 is a flow diagram of an embodiment of a method 600 for supplyingprimary fuel and secondary fuel to a reciprocating-piston engine, forexample, associated with a hydraulic fracturing unit of a hydraulicfracturing system, according to embodiments of the disclosure. In someexamples, the method 600 may be performed semi- or fully-autonomously,for example, via a controller. The method 600 may be utilized inassociation with various systems, such as, for example, the examplesystem 28 shown in one or more of FIGS. 1 and 2 .

The example method 600, at 602, may include determining a total powerload on the reciprocating-piston engine due to operation of hydraulicauxiliary components supplied with power by the reciprocating-pistonengine and/or electrical auxiliary components supplied with power by thereciprocating-piston engine. For example, a controller may receive oneor more signals indicative of operation of one or more of the hydraulicauxiliary components or the electrical auxiliary components, forexample, as described previously herein. In some examples, the one ormore signals may include one or more signals generated by one or moresensors associated with the hydraulic auxiliary components or theelectrical auxiliary components.

At 604, the example method 600 may further include determining a firstamount of primary fuel to supply to the reciprocating-piston engine anda second amount of secondary fuel to supply to the reciprocating-pistonengine, for example, based at least in part on the total power load. Forexample, the controller may be configured determine the first amount andthe second amount based at least in part on an efficiency of the primaryfuel relative to an efficiency of the secondary fuel, for example, asdescribed previously herein. In some examples, the controller may beconfigured to determine the first amount and the second amount based atleast in part on first expected emissions generated during operation ofthe reciprocating-piston engine using the first amount of primary fuelor second expected emissions generated during operation of thereciprocating-piston engine using the second amount of secondary fuel,for example, as previously described herein.

At 606, the example method 600 may also include causing a primary valveto operate to supply the first amount of primary fuel to thereciprocating-piston engine, for example, based at least in part on thefirst amount of the primary fuel and the second amount of the secondary.For example, the controller may be configured to cause the primary valveto open and/or meter primary fuel to supply the reciprocating-pistonengine, for example, as described previously herein.

The example method 600, at 608, may further include causing a fuel pumpand/or a secondary valve to operate to supply the second amount ofsecondary fuel to the reciprocating-piston engine, for example, based atleast in part on the first amount of the primary fuel and the secondamount of the secondary. For example, the controller may be configuredto cause the fuel pump and/or the secondary valve to open and/or metersecondary fuel to supply the reciprocating-piston engine, for example,as described previously herein.

The example method 600, at 610, may also include causing thereciprocating-piston engine to operate according to two or more phases,depending at least in part on the total power load.

For example, at 612, the example method 600 may also include determiningwhether using a combination of the first amount of primary fuel and thesecond amount of the secondary fuel provides a power output at leastequal to the total power load. For example, the controller may determinewhether the primary fuel has enough energy per unit mass to provide anamount of energy sufficient to supply the reciprocating piston-engine toprovide a power output at least equal to the total power load. If so, acombination of the primary fuel and secondary fuel may be used to supplythe reciprocating-piston engine.

If, at 612, it has been determined that using a combination of the firstamount of primary fuel and the second amount of the secondary fuelprovides a power output at least equal to the total power load, at 614,the example method 600 may further include determining the first amountof primary fuel and the second amount of secondary fuel based at leastin part on considerations related to efficiency and/or emissions. Forexample, the considerations may relate to a first efficiency of theprimary fuel, a second efficiency of the secondary fuel, a firstexpected emissions generated during operation of thereciprocating-piston engine using the first amount of primary fuel,and/or a second expected emissions generated during operation of thereciprocating-piston engine using the second amount of secondary fuel.For example, the controller may be configured to access tables and orperform calculations to determine a combination of the first amount ofprimary fuel and the second amount of secondary fuel to provide a poweroutput sufficient to meet the power demand corresponding to the totalpower load, for example, as described previously herein.

If, at 612, it has been determined that using a combination of the firstamount of primary fuel and the second amount of the secondary fuel willnot provide a power output at least equal to the total power load, at616, however, the example method 600 further may include operating thereciprocating-piston engine using solely the secondary fuel. Forexample, as described above, the controller may determine that it is notpossible to meet the total power load demand using any of the primaryfuel and determine that the reciprocating-piston engine should beoperated using solely the secondary fuel, which may produce more powerthan the primary fuel.

It should be appreciated that subject matter presented herein may beimplemented as a computer process, a computer-controlled apparatus, acomputing system, or an article of manufacture, such as acomputer-readable storage medium. While the subject matter describedherein is presented in the general context of program modules thatexecute on one or more computing devices, those skilled in the art willrecognize that other implementations may be performed in combinationwith other types of program modules. Generally, program modules includeroutines, programs, components, data structures, and other types ofstructures that perform particular tasks or implement particularabstract data types.

Those skilled in the art will also appreciate that aspects of thesubject matter described herein may be practiced on or in conjunctionwith other computer system configurations beyond those described herein,including multiprocessor systems, microprocessor-based or programmableconsumer electronics, minicomputers, mainframe computers, handheldcomputers, mobile telephone devices, tablet computing devices,special-purposed hardware devices, network appliances, and the like.

The controller 80 can include one or more industrial control systems(ICS), such as supervisory control and data acquisition (SCADA) systems,distributed control systems (DCS), and/or programmable logic controllers(PLCs). For example, the controller 80 may include one or moreprocessors, which may operate to perform a variety of functions, as setforth herein. In some examples, the processor(s) may include a centralprocessing unit (CPU), a graphics processing unit (GPU), both CPU andGPU, or other processing units or components. Additionally, at leastsome of the processor(s) may possess local memory, which also may storeprogram modules, program data, and/or one or more operating systems. Theprocessor(s) may interact with, or include, computer-readable media,which may include volatile memory (e.g., RAM), non-volatile memory(e.g., ROM, flash memory, miniature hard drive, memory card, or thelike), or some combination thereof. The computer-readable media may benon-transitory computer-readable media. The computer-readable media maybe configured to store computer-executable instructions, which whenexecuted by a computer, perform various operations associated with theprocessor(s) to perform the operations described herein.

Example embodiments of the controller 70 may be provided as a computerprogram item including a non-transitory machine-readable storage mediumhaving stored thereon instructions (in compressed or uncompressed form)that may be used to program a computer (or other electronic device) toperform processes or methods described herein. The machine-readablestorage medium may include, but is not limited to, hard drives, floppydiskettes, optical disks, CD-ROMs, DVDs, read-only memories (ROMs),random access memories (RAMs), EPROMs, EEPROMs, flash memory, magneticor optical cards, solid-state memory devices, or other types ofmedia/machine-readable medium suitable for storing electronicinstructions. Further, example embodiments may also be provided as acomputer program item including a transitory machine-readable signal (incompressed or uncompressed form). Examples of machine-readable signals,whether modulated using a carrier or not, include, but are not limitedto, signals that a computer system or machine hosting or running acomputer program can be configured to access, including signalsdownloaded through the Internet or other networks.

Having now described some illustrative embodiments of the disclosure, itshould be apparent to those skilled in the art that the foregoing ismerely illustrative and not limiting, having been presented by way ofexample only. Numerous modifications and other embodiments are withinthe scope of one of ordinary skill in the art and are contemplated asfalling within the scope of the disclosure. In particular, although manyof the examples presented herein involve specific combinations of methodacts or system elements, it should be understood that those acts andthose elements may be combined in other ways to accomplish the sameobjectives. Those skilled in the art should appreciate that theparameters and configurations described herein are exemplary and thatactual parameters and/or configurations will depend on the specificapplication in which the systems and techniques of the invention areused. Those skilled in the art should also recognize or be able toascertain, using no more than routine experimentation, equivalents tothe specific embodiments of the invention. It is, therefore, to beunderstood that the embodiments described herein are presented by way ofexample only and that, within the scope of any appended claims andequivalents thereto, the embodiments of the disclosure may be practicedother than as specifically described.

This is a continuation of U.S. Non-Provisional application Ser. No.17/663,294, filed May 13, 2022, titled “BI-FUEL RECIPROCATING ENGINE TOPOWER DIRECT DRIVE TURBINE FRACTURING PUMPS ONBOARD AUXILIARY SYSTEMSAND RELATED METHODS,” which is a continuation of U.S. Non-Provisionalapplication Ser. No. 17/653,893, filed Mar. 8, 2022, titled “BI-FUELRECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINE FRACTURING PUMPSONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” now U.S. Pat. No.11,365,616, issued Jun. 21, 2022, which is a continuation of U.S.Non-Provisional application Ser. No. 17/481,794, filed Sep. 22, 2021,titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINEFRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” nowU.S. Pat. No. 11,313,213, issued Apr. 26, 2022, which is a divisional ofU.S. Non-Provisional application Ser. No. 17/301,241, filed Mar. 30,2021, titled “BI-FUEL RECIPROCATING ENGINE TO POWER DIRECT DRIVE TURBINEFRACTURING PUMPS ONBOARD AUXILIARY SYSTEMS AND RELATED METHODS,” nowU.S. Pat. No. 11,208,880, issued Dec. 28, 2021, which claims priority toand the benefit of, under 35 U.S.C. § 119(e), U.S. ProvisionalApplication No. 62/705,188, filed Jun. 15, 2020, titled “BI-FUELRECIPROCATING ENGINE TO POWER ONBOARD FRACTURING PUMP AUXILIARY SYSTEMSAND RELATED METHODS,” and U.S. Provisional Application No. 62/704,774,filed May 28, 2020, titled “SYSTEMS AND METHODS FOR SUPPLYING PRIMARYFUEL AND SECONDARY FUEL TO AN INTERNAL COMBUSTION ENGINE OF A FRACTURINGUNIT,” the disclosures of which are incorporated herein by reference intheir entireties.

Furthermore, the scope of the present disclosure shall be construed tocover various modifications, combinations, additions, alterations, etc.,above and to the above-described embodiments, which shall be consideredto be within the scope of this disclosure. Accordingly, various featuresand characteristics as discussed herein may be selectively interchangedand applied to other illustrated and non-illustrated embodiment, andnumerous variations, modifications, and additions further can be madethereto without departing from the spirit and scope of the presentinvention as set forth in the appended claims.

What is claimed is:
 1. A system to supply primary fuel and secondaryfuel to operate one or more engines, the system comprising: a firstmanifold positioned to provide fluid flow from a primary fuel source ofprimary fuel to the one or more engines; a second manifold positioned toprovide fluid flow from a secondary fuel supply of secondary fuel to theone or more engines; one or more of: (a) a fuel pump positioned to pumpfluid between the secondary fuel source and the one or more engines, or(b) one or more valves, associated with the second manifold andpositioned to allow fluid flow between the secondary fuel source and theone or more engines when in an open position; and a controller incommunication with one or more of the valves or the fuel pump andconfigured to: receive one or more signals indicative of power load onthe one or more engines; determine, based at least in part on one ormore signals indicative of power load on the one or more engines, atotal power load; determine, based at least in part on the total powerload, a first amount of primary fuel to supply to the one or moreengines and a second amount of secondary fuel to supply to the one ormore engines; and cause, based at least in part on the first amount andthe second amount, one or more of: (a) the one or more valves, or (b)the fuel pump, to operate to supply the first amount of primary fuel andthe second amount of secondary fuel to the one or more engines.
 2. Thesystem of claim 1, wherein the first amount of primary fuel increasesrelative to the second amount of secondary fuel as the total power loadincreases up to a first total power load and decreases relative to thesecond amount of secondary fuel as the total power load increases beyondthe first total power load.
 3. The system of claim 1, wherein thecontroller further is configured to determine the first amount and thesecond amount based at least in part on an efficiency of the primaryfuel relative to an efficiency of the secondary fuel.
 4. The system ofclaim 3, wherein the controller further is configured to determine thefirst amount and the second amount based at least in part on one or moreof: efficiency data determined by correlating one or more of theefficiency of the primary fuel, the efficiency of the secondary fuel, orpower output of the one or more engines operating by use of the primaryfuel and the secondary fuel; or a mathematical function relating theefficiency of the primary fuel, the efficiency of the secondary fuel,and the power output of the one or more engines by use of the primaryfuel and the secondary fuel.
 5. The system of claim 1, wherein thecontroller further is configured to determine the first amount and thesecond amount based at least in part on one or more of (a) firstexpected emissions generated during operation of the one or more enginesby use of the first amount of primary fuel or (b) second expectedemissions generated during operation of the one or more engines by useof the second amount of secondary fuel.
 6. The system of claim 5,wherein the controller further is configured to determine the firstamount and the second amount based at least in part on one or more of:emissions data from a table correlating one or more of the firstexpected emissions, the second expected emissions, or power output ofthe one or more engines operating by use of the primary fuel and thesecondary fuel; or a formula relating the first expected emissions, thesecond expected emissions, and the power output of the one or moreengines by use of the primary fuel and the secondary fuel.
 7. The systemof claim 1, wherein the controller further is configured to cause theone or more engines to operate according to two or more phases,depending at least in part on the total power load, the two or morephases comprising: a first phase during which operation of the one ormore engines by use of a combination of the first amount of primary fueland the second amount of secondary fuel provides a power output at leastequal to the total power load; and a second phase when the total powerload is greater than a maximum amount of power output that the one ormore engines is capable of producing by use of a combination of theprimary fuel and the secondary fuel, and during which the one or moreengines operates by use solely of the secondary fuel.
 8. The system ofclaim 7, wherein during operation of the one or more engines accordingto the first phase, the controller further is configured to determinethe first amount and the second amount based at least in part on one ormore of a first efficiency of the primary fuel, a second efficiency ofthe secondary fuel, a first expected emissions generated duringoperation of the one or more engines by use of the first amount ofprimary fuel, or a second expected emissions generated during operationof the one or more engines by use of the second amount of secondaryfuel.
 9. The system of claim 1, further comprising: a pressure regulatorassociated with the first manifold upstream of the primary valve; and afilter positioned to separate one of more of particulates or fluids fromthe primary fuel upstream of the pressure regulator.
 10. The system ofclaim 1, wherein: the one or more engines comprise a first internalcombustion engine, and the first manifold provides fluid flow from theprimary fuel source of primary fuel to a second internal combustionengine.
 11. The system of claim 1, wherein one or more of: the firstmanifold is positioned to provide fluid flow between the primary fuelsource and an air intake manifold of the one or more engines; or thesecond manifold is positioned to provide fluid flow between thesecondary fuel supply and one or more combustion chambers of the one ormore engines.
 12. The system of claim 1, wherein the second manifold ispositioned to provide fluid flow between the secondary fuel supply andone or more fuel injectors.
 13. The system of claim 1, wherein the powerload comprises one or more of (a) one or more hydraulic pumps, or (b)one or more electrical power generating devices.
 14. The system of claim1, wherein the one or more signals indicative of one or more of thepower load on the one or more engines comprises one or more signalsgenerated by one or more sensors associated with operation of one ormore of hydraulic auxiliary components supplied with power by the one ormore engines or electrical auxiliary components supplied with power bythe one or more engines.
 15. The system of claim 1, wherein the primaryfuel comprises a gaseous fuel and the secondary fuel comprises a liquidfuel.
 16. A fracturing unit comprising: a chassis; a turbine engineconnected to the chassis and positioned to convert fuel into a poweroutput for operating one or more fracturing pumps; areciprocating-piston engine connected to the chassis and positioned tosupply power to operate one or more of auxiliary components associatedwith a fracturing unit; a first manifold positioned to provide fluidflow from a primary fuel source of primary fuel to the turbine engineand the reciprocating-piston engine; a second manifold positioned toprovide fluid flow from a secondary fuel supply of secondary fuel to thereciprocating-piston engine; and a controller configured to: determine afirst amount of primary fuel to supply to the reciprocating-pistonengine and a second amount of secondary fuel to supply to thereciprocating-piston engine; and cause supply of the first amount ofprimary fuel and the second amount of secondary fuel to thereciprocating-piston engine.
 17. The fracturing unit of claim 16,further comprising one or more of: (a) a primary valve associated withthe first manifold and positioned to allow fluid flow between theprimary fuel source and the reciprocating-piston engine when in an openposition, and wherein the controller further is configured to cause theprimary valve to supply the first amount of primary fuel to thereciprocating-piston engine; or (b) one or more of: (i) a fuel pump, or(ii) a secondary valve, associated with the second manifold andpositioned to allow fluid flow between the secondary fuel source and thereciprocating-piston engine when in an open position, and wherein thecontroller further is configured to cause one or more of: (x) the fuelpump, or (y) the secondary valve, to supply the second amount ofsecondary fuel to the reciprocating-piston engine.
 18. The fracturingunit of claim 16, wherein the one or more auxiliary components comprisesone or more of: (a) hydraulic auxiliary components comprising ahydraulic pump positioned to supply hydraulic power to the fracturingunit, and wherein the one or more signals indicative of operation of thehydraulic auxiliary components comprises one or more signals indicativeof a hydraulic power load on the reciprocating-piston engine viaoperation of the hydraulic pump; or (b) electrical auxiliary componentscomprising an electrical power generation device to supply electricalpower to the fracturing unit, and wherein the one or more signalsindicative of operation of the electrical auxiliary components comprisesone or more signals indicative of an electric power load on thereciprocating-piston engine via operation of the electrical powergeneration device.
 19. The fracturing unit of claim 16, wherein thecontroller further is configured to determine, based at least in part onthe one or more signals, a total power load on the reciprocating-pistonengine, and wherein the first amount of primary fuel increases relativeto the second amount of secondary fuel as the total power load increasesup to a first total power load and decreases relative to the secondamount of secondary fuel as the total power load increases beyond thefirst total power load.
 20. The fracturing unit of claim 16, wherein thecontroller further is configured to determine the first amount and thesecond amount based at least in part on one or more of: efficiency datadetermined from correlating one or more of the efficiency of the primaryfuel, the efficiency of the secondary fuel, or power output of thereciprocating-piston engine operating by use of the primary fuel and thesecondary fuel; or a mathematical function relating the efficiency ofthe primary fuel, the efficiency of the secondary fuel, and the poweroutput of the reciprocating-piston engine by use of the primary fuel andthe secondary fuel.
 21. The fracturing unit of claim 16, wherein thecontroller further is configured to determine the first amount and thesecond amount based at least in part on one or more of first expectedemissions generated during operation of the reciprocating-piston engineby use of the first amount of primary fuel or second expected emissionsgenerated during operation of the reciprocating-piston engine by use ofthe second amount of secondary fuel.
 22. The fracturing unit of claim21, wherein the controller further is configured to determine the firstamount and the second amount based at least in part on one or more of:emissions data determine from correlating one or more of the firstexpected emissions, the second expected emissions, or power output ofthe reciprocating-piston engine operating by use of the primary fuel andthe secondary fuel; or a mathematical function relating the firstexpected emissions, the second expected emissions, and the power outputof the reciprocating-piston engine by use of the primary fuel and thesecondary fuel.
 23. The fracturing unit of claim 16, further comprisingone or more of: a primary valve associated with the first manifold andpositioned to allow fluid flow between the primary fuel source and thereciprocating-piston engine when in an open position; or a secondaryvalve associated with the second manifold and positioned to allow fluidflow between the secondary fuel source and the reciprocating-pistonengine when in an open position, and wherein one or more of the primaryvalve or the secondary valve comprises a metering valve.
 24. Thefracturing unit of claim 16, wherein the controller further isconfigured to determine, based at least in part on the one or moresignals, a total power load on the reciprocating-piston engine, andwherein the controller further is configured to cause thereciprocating-piston engine to operate according to two or more phases,depending at least in part on the total power load, the two or morephases comprising: a first phase during which operation of the whereinthe controller further is configured to determine, based at least inpart on the one or more signals, a total power load on thereciprocating-piston engine by use of a combination of the first amountof primary fuel and the second amount of secondary fuel provides a poweroutput at least equal to the total power load; and a second phase whenthe total power load is greater than a maximum amount of power outputthat the wherein the controller is configured to determine, based atleast in part on the one or more signals, a total power load on thereciprocating-piston engine is capable of producing by use of acombination of the primary fuel and the secondary fuel, and during whichthe controller further is configured to determine, based at least inpart on the one or more signals, a total power load on thereciprocating-piston engine operates by use of solely the secondaryfuel, and wherein during operation of the reciprocating-piston engineaccording to the first phase, the controller further is configured todetermine the first amount and the second amount based at least in parton one or more of a first efficiency of the primary fuel, a secondefficiency of the secondary fuel, a first expected emissions generatedduring operation of the reciprocating-piston engine by use of the firstamount of primary fuel, or a second expected emissions generated duringoperation of the reciprocating-piston engine by use of the second amountof secondary fuel.
 25. A fracturing unit comprising: a chassis; aturbine engine connected to the chassis and positioned to convert fuelinto a power output; a reciprocating-piston engine connected to thechassis and positioned to supply power to operate one or more auxiliarycomponents associated with the fracturing unit; a first manifoldpositioned to provide fluid flow from a primary fuel source of primaryfuel to the turbine engine and the reciprocating-piston engine; and acontroller configured to: determine, based at least in part on one ormore signals, a first amount of primary fuel to supply to thereciprocating-piston engine and a second amount of secondary fuel tosupply to the reciprocating-piston engine; and cause, based at least inpart on the first amount and the second amount, supply of the firstamount of primary fuel and the second amount of secondary fuel to thereciprocating-piston engine.
 26. The fracturing unit of claim 25,further comprising: one or more of: (a) a fuel pump, or (b) a valve,associated with the second manifold and positioned to allow fluid flowbetween the secondary fuel source and the reciprocating-piston enginewhen in an open position, wherein the controller is configured to causeone or more of: (x) the fuel pump, or (y) the valve, to supply thesecond amount of secondary fuel to the reciprocating-piston engine. 27.The fracturing unit of claim 25, wherein the controller further isconfigured to determine, based at least in part on the one or moresignals, a total power load on the reciprocating-piston engine, andwherein the first amount of primary fuel increases relative to thesecond amount of secondary fuel as the total power load increases up toa first total power load and decreases relative to the second amount ofsecondary fuel as the total power load increases beyond the first totalpower load.
 28. The fracturing unit of claim 27, wherein the controllerfurther is configured to determine the first amount and the secondamount based at least in part on one or more of: efficiency datadetermined from correlating one or more of the efficiency of the primaryfuel, the efficiency of the secondary fuel, or power output of thereciprocating-piston engine operating by use of the primary fuel and thesecondary fuel; or a mathematical function relating the efficiency ofthe primary fuel, the efficiency of the secondary fuel, and the poweroutput of the reciprocating-piston engine by use of the primary fuel andthe secondary fuel.
 29. The fracturing unit of claim 28, wherein thecontroller further is configured to determine the first amount and thesecond amount based at least in part on one or more of first expectedemissions generated during operation of the reciprocating-piston engineby use of the first amount of primary fuel or second expected emissionsgenerated during operation of the reciprocating-piston engine by use ofthe second amount of secondary fuel.